Compensation method and process of high-power laser thermal lensing effect

Background technology:

High-power all-solid-state lasers and amplifiers have a wide range of important applications in scientific research, military, medicine and laser micro-nano processing, with the advantages of high efficiency, low cost, small size and good stability. All-solid-state lasers with high power and high beam quality have great scientific significance and application value.

In high-power laser systems, the laser gain medium is often pumped by high-power lasers, so that the laser crystal exhibits a thermal lensing effect, which affects the beam quality of the laser output. At the same time, due to the thermal effect, the stability region of the laser will be narrowed, which is not conducive to the output of high-power lasers.

In lasers and amplifiers based on solid-state laser gain media, most of the laser crystals used in the existing laser structures are not isotropic. Due to the anisotropy of the laser gain medium, the thermal focal length of the optical axis and non-optical axis directions is often inconsistent in the case of pumped laser pumping. The inconsistency of the thermal focal length in the optical and non-optical directions will lead to the narrowing of the stable region of the original laser and the introduction of astigmatism.

In order to suppress the thermal effects in the laser amplifier process, there are two methods currently used:

The first is to use cryogenic cooling, by building a low-temperature chamber and vacuum treatment, placing liquid nitrogen to cool the laser crystal at low temperature. This method can effectively suppress the thermal lensing effect, but the economic cost of liquid nitrogen cooling is large and the process is very complex.

The second is to design the cavity type of the laser, so that the stable region of the laser can tolerate inconsistent thermal focal lengths. However, this method cannot fundamentally solve the astigmatism introduced by the inconsistent thermal focal length, and will lead to the reduction of laser stability. Therefore, there is an urgent need for a simpler and more effective compensation method for the suppression of thermal effects of high-power lasers and laser amplifiers.

Technical implementation elements:

An object of the present invention is to overcome the limitation of the above-mentioned existing suppression of the thermal effect of high-power laser, and to provide a compensation method for the thermal lensing effect of high-power laser, which can effectively suppress the thermal lensing effect of high-power laser, and the method is not only simple to operate, scientific and effective, but also has strong practicability.

The technical solution of the present invention is as follows:

The compensation method of the high-power laser thermal lensing effect, the original laser structure comprises a pump laser, and the output direction of the pump laser is a beam splitter, the beam splitter will divide the input laser into 50% of the reflected light and the transmitted light respectively, in the transmitted light direction is the first dichroic mirror, the first laser crystal, the second laser crystal, the second dichroic mirror, the laser output mirror, in the direction of the reflected light is the first all-reflective mirror, the second all-reflective mirror, the third all-reflective mirror, the second dichroic mirror, the second laser crystal, the first laser crystal, laser cavity mirror, the first laser crystal and the second laser crystal are placed in the same direction according to the crystal axis direction of the factory identification, and the laser cavity mirror, the first dichroic mirror, the second dichroic mirror, and the laser output mirror constitute a laser resonator. The method consists of the following steps:

rotate the second laser crystal, make the crystal axis direction of the manufacturer identification of the second laser crystal perpendicular to each other with the crystal axis direction of the manufacturer identification of the first laser crystal, add a one-half glass slide in the middle of the first laser crystal and the second laser crystal, turn on the laser power supply, measure the output laser beam at one end of the laser output mirror through CCD, fine-tune the crystal axis direction of described second laser crystal simultaneously, and complete fine-tuning when the beam output by CCD measuring laser is circular.

The first laser crystal and the second laser crystal are identical except that the placement direction keeps the optical axis orthogonal of the two laser crystals.

The polarization states of the laser rays of the input first laser crystal and the second laser crystal are parallel to the optical axis directions of the first laser crystal and the second laser crystal respectively.

The principle of the present invention is:

High beam quality, high power laser output is essential for subsequent applications. The anisotropy of the laser crystal leads to the inconsistency of the thermal focal length in the orthogonal direction, which brings about the astigmatism of the laser beam and affects the subsequent laser focusing intensity. In addition, the inconsistency of the thermal focal length in the orthogonal direction of the laser crystal will also lead to the narrowing of the range of the laser stabilization area, which will reduce the long-term working stability of the laser. The present invention adopts two laser crystals placed orthogonally in the direction of the optical axis, and compensates for the difference of the thermal lens of the laser crystal in the direction of the optical axis and the non-optical axis direction by changing the laser polarization state incident on the two crystals, and fundamentally avoids the inconsistency of the thermal focal length of the two orthogonal directions in the uniaxial crystal.

Compared with the prior art, the present invention has the following significant features:

1. The invention makes the crystal axis direction of the second laser crystal perpendicular to each other with the crystal axis direction of the first laser crystal, adds a one-half glass slide in the middle of the first laser crystal and the second laser crystal, does not need to use low temperature or vacuum equipment, and compensates for the high-power laser thermal lensing effect very simply and effectively;

2. The present invention utilizes two pieces of orthogonally placed laser crystals, fundamentally avoids astigmatism, and reduces the difficulty of laser cavity design;

3. The invention broadens the stable area range of the laser, and greatly improves its long-term stability.

4. The experiment shows that the spot output by the laser of the present invention is circular, and the spot output by the original structure laser (see Fig. 1) is an elliptical spot, and the method of the present invention can well suppress the high-power laser thermal lensing effect, that is, the high-power laser thermal lensing effect has been compensated.